The present invention relates to an information insertion/detection system for discrete cosine transform (DCT) coefficients coping with resolution conversion, and in particular, to an information insertion/detection system for discrete cosine transform (DCT) coefficients associated with an image size of video signals.
To compress an image and/or voice, the discrete cosine transform has been recently adopted. In the technique, signals are encoded through an orthogonal transform process as an efficient encoding operation into signals of respective coefficients. Coefficients which resultantly have no correlation therebetween are encoded. In general, for example, Fourier transform, Hadamard transform, or K-L transform is known for the transforming technique. However, thanks to improvement of processing performance of devices due to recent development of the device technique, an efficient discrete cosine transform has been primarily utilized. Also in moving picture expert group (MPEG) 1, MPEG 2, MPEG 4, and MPEG 7 employing a DCT operation for image or video signals and for voice or audio signals, the conversion technique has been employed in a hybrid system in combination with a forecasting device.
In the MPEG image compression/expansion encoding method of the prior art, an original image is subdivided into blocks each of which including data of 8 pixels by 8 pixels. A DCT operation is conducted for the blocks to produce direct-current (dc) signal components and alternating-current (ac) signal components. The dc and ac components are alternately outputted to a quantizing unit in an ascending order of frequency, namely, beginning from a lower-frequency component to high frequency component. The quantizing unit quantizes the received signal components utilizing a predetermined luminance signal quantization table and a predetermined color difference signal quantization table. Signals resultant from the quantization are transmitted therefrom as DCT coefficients. In MPEG1 technique, bit streams of the quantized signals are sent through a sequence layer of a group of picture (GOP) layer, a picture layer, a slice layer, a macro block layer, and a block layer. The DCT coefficients after the DCT operation are fed to the block layer in the form of quantized numeric values. The quantized values are represented according to a run level of a first DCT coefficient thereof, a variable-length code of the level, and a difference between the first DCT coefficient and a DCT coefficient subsequent thereto.
MPEG2, same as in MPEG1, are six layers ranging from the sequence layer to the block layer. MPEG2 uses a bit stream similar to that of MPG1. However, when a sequence extension field appears subsequently a sequence header, the signals are determined as MPEG2 signals. In the block layer, SDC (Subsequent DCT Coefficients) signals are sent in a bit stream including a DCT DC size luminancexe2x80x94DCT DC differential (DDSL-DDD) field, a DCT DC size chrominancexe2x80x94DCT DC differential (DDSC-DDD) field, a first DCT coefficient (FDC) field, a subsequent DCT coefficients (field), and an end of block (EOB) field. The DCT coefficients are quantized as follows. DCT coefficients are scanned in the block layer according to dc components thereof in an alternating manner in the block layer. The DCT coefficients are then quantized using a quantization table to obtain differences therebetween. The differences are transmitted in the form of a quantity of data.
However, in the DCT information insertion step, information is inserted into each MPEG block. Therefore, when a picture or an image is expanded or minimized after the insertion of DCT coefficients, there possibly occurs a case in which the information of DCT coefficients cannot be detected. In the expansion or compression of video signals, when the transmission capacity of a communication line is insufficient, for example, in a case of radio transmission, the picture signals are compressed before transmission depending on cases.
In this situation, the video signals are compressed after insertion of information in DCT coefficients. Consequently, the information of DCT coefficients cannot be easily detected in the information of DCT signals inserted into the video signals sent via radio transmission. Moreover, when the video signals are expanded or compressed through an illegal action, it is impossible to detect information of the DCT coefficients. Consequently, a considerable need exists for an information inserter and an information detector for the DCT coefficients coping with signal expansion and compression.
It is therefore an object of the present invention to provide an information insertion/detection system in which even when a video signal with DCT coefficients inserted therein is expanded and/or compressed, the DCT coefficients can be correctly restored to be inserted in a video signal.
To achieve the object above in accordance with the present invention, there is provided a system in which information is inserted in DCT coefficients so that the information can be detected by referring to an image size of MPEG data inputted to the system when the image data is converted into a reference image size. In the detection of the information in the DCT coefficients, an information detector of the information of DCT coefficients refers to a picture size of MPEG data to be detected and carries out processing equivalent to the method of reference picture size conversion described above. An information inserter and an information detector for the information of CDT coefficients conduct processing according to an equal reference picture size. Therefore, the information of DCT coefficients can be detected regardless of the image size in the insertion of information in the DCT coefficients and independent of conversion of resolution after the insertion.
In accordance with the present invention, there is provided an information insertion/detection system for detecting and inserting DCT coefficients in image signals. The system includes a resolution analyzer for receiving image code data and outputting the image code data and information of size of an image of the image code data, an insertion pattern determining unit for receiving the image code data and the image size information and outputting the image code data and pattern information, an information inserter for receiving the image code data and the pattern information and producing image code data by inserting information of the DCT coefficients into the image code data, and a video analyzer for receiving the image code data and producing information of insertion strength of the DCT coefficients.
In accordance with the present invention, there is provided an information insertion/detection system for detecting and inserting DCT coefficients in image signals. The system includes a resolution analyzer for receiving image code data of the image signals and outputting the image code data and image size information of the image code data, a block expander for receiving the image code data and the image size information and outputting DCT coefficients of the image code data and the image code data, a DCT coefficient buffer for receiving the DCT coefficients and outputting, when one frame of DCT coefficients is accumulated, an information detection start signal of the DCT coefficients accumulated therein, and a DCT coefficient information detector for detecting information in the DCT coefficients in response to the information detection start signal and outputting a result of the detection.
Conceptually, the system can detect, even after the insertion of information into DCT coefficients, the information inserted into DCT coefficients. In the prior art, when video resolution is converted or changed after the insertion of information into DCT coefficients, it is difficult to detect the inserted information. In contrast therewith, the present invention provides an information insertion/detection system for DCT coefficients coping with picture expansion and minimization only by slightly modifying the information inserter and the information detector for information of DCT coefficients.